The financial services company will become principal sponsor of the national team from the start of the 2010/11 season, as part of an initial three-year deal brokered by Essentially.
Admiral will become shirt sponsor and its logo will appear on all secondary and training apparel. The deal also includes in-stadia signage, tickets to matches and access to international players.
Charlotte Bennett, marketing director at Admiral said: "This is the first time Admiral has entered into sport sponsorship, but as a proud Welsh company there is no one better for us to sponsor than the Welsh national team.
"We look forward to a successful partnership with the WRU and the benefits we will see from our association with them. And I'm sure our employees will be thrilled to see the Admiral logo on the new team kit."
The deal was announced prior to the Wales V Italy RBS Six Nations match at the Millennium Stadium in Cardiff on Saturday.
Admiral is part of the Admiral Group, which also incorporates Confused.com, Elephant.co.uk and Diamond.